Process Planning Episode 1 pot

This means that the manufacturing of the products must be planned to make best use of these resources, which is the very essence of process planning... 2 Process Planning 1.2 Aims and ob

Process Planning:

The design/manufacture interface

Preface

Most prefaces tend to focus on the technical content of the textbook, why the author felt the need to write it, what makes it different and most of all why readers should buy it However, this was such an extraordinary learning experience for me, that I thought I should share some of it with you Near the end of session 1998-9, I was asked as Programme Leader for a then HND/BSc Manufacturing to consider revamping the course During the process of developing this new programme, the focus of which was manu- facturing management and in particular manufacturing planning and control,

I was developing a curriculum for a module on process planning As part

of this, a number of references for library resources had to be identified Although there were many fine textbooks on computer-aided process plan- ning and for postgraduate research, there appeared to be none that were par- ticularly suitable for undergraduate study Furthermore, as the emphasis of the module was on the skills and knowledge required for process planning and not on the technology, I needed a textbook that was easy for undergrad- uates to follow while being reasonably thorough

Having contacted a number of publishers, it became apparent that here was an excellent opportunity to write and publish my first book After all,

I had written and published distance learning material and how difficult could it be? If only I knew then what I know now! Having estimated that it would take me about eighteen months to write the book, I finally finished in October of 2002, 18 months late! During this time there was a major illness

in the family, a car written off, a disastrous house move, the birth of our fifth daughter (not a typing error I hasten to add!) and so many changes with my job that would require a book for themselves However imperfect it may be,

I was determined to finish it and here it is!

Finally, I make no apologies for the fact that I haven't been strictly stick- ing to conventions for technical writing or the fact that the odd colloquialism has crept in This is because the intended audience for this book is not other academics, but students I wanted it to be learner-friendly, which in my experience, many academics aren't!

Peter Scallan October 2002

Acknowledgements

There are many fine people and organizations that I must thank in the pre- paration of this manuscript In an effort to ensure that I don't miss anybody out, I have categorized these under three headings, namely reviewers, picture credits and personal

Reviewers First in the list are the friends and colleagues who unwittingly volunteered

to review chapters for me as follows:

Dr Arthur Loughran, Senior Lecturer, Centre for Learning and Teaching, University of Paisley (Chapters 1-4);

Mr Alex Neil, Lecturer, Faculty of Engineering, Kilmarnock College (Chapters 5 and 6);

Mr John Hunter, Lecturer, Division of Design & Engineering, University of Paisley (Chapters 7 and 10);

Mr David Smyth, Senior Lecturer, Division of Design & Engineering, University of Paisley (Chapters 8 and 9)

Your comments and contributions were invaluable and greatly appreci- ated I tried to incorporate as much of your suggestions as possible I am forever in your debt or at least I owe you a pint (or eight in John's case!)

Picture and figure credits A number of individuals and their associated organizations also deserve

mention for their help and allowing me to use material as follows:

Tine Stalmans, Palgrave MacMillan: Figure 1.16 and Case study 1.1 Adapted and reproduced from Coward, David G Manufacturing Management: Learning through Case Studies, 1998, Macmillan Press with

permission of Palgrave Macmillan

Gordon Mair, Senior Lecturer, DMEM, University of Strathclyde: Figures 1.3, Q3.3, 4.22, 5.15, Q5.2, Q10.2 and Case study 4.1 Reprinted and adapted with the authors permission from Mastering Manufacturing by Gordon Mair

Peter Hogarth, University of Bournemouth: Figure 3.1 Diagram adapted and reproduced with permission from Peter Hogarth on behalf of SEED (Shared Experience in Engineering Design) Website:www.seed.co.uk Permissions Dept at Elsevier Science: Figures 3.5, 3.7, 3.15 Reproduced/adapted from Beginning AutoCAD by Bob McFarlane Figure

3.14 Reproduced/adapted from Beginning AutoCAD 2000 by Bob

McFarlane Figure 3.23 and Case study 3.1 adapted from Case Studies in Engineering Design by C Matthews Figures 4.7, 5.1, 5.2, 5.4, 5.8-5.11,

Acknowledgements xi

5.14, 5.19, 5.20, 5.22, 5.23, 5.26-5.32 Reproduced from Process Selection

- From Design to Manufacture by K.G Swift and J.D Booker Figures 5.12,

5.13 and 5.18 Reproduced from Principles of Metal Manufacturing Processes by J Beddoes and M.J Bibby Figures 5.16 and 5.17 Reproduced

from Principles of Engineering Manufacture by S.C Black, V Chiles,

A.J Lissaman and S.J Martin Case study 2.2 Adapted and reproduced from

Operations Management in Context by L Galloway, E Rowbotham and

M Azhashain All reprinted by permission of Elsevier Science

Mark Endean, Lyndon Edwards and Richard McCracken, The Open University: Table 4.1, 4.11 and Case study 4.2 Adapted and reproduced with the kind permission of The Open University, Walton Hall, Milton Keynes, MK7 6AB Website: www.open.ac.uk

WDS: Figures 7.1, 7.41, 7.42, 7.43, 7.45-7.55, 7.59, 7.60 All pictures and diagrams used by kind permission of WDS, Richardshaw Road, Grangefield Industrial Estate, Pudsey, Leeds LS28 9LE Website: www.wdsltd.co.uk Email: sales @wdsltd.co.uk

Carr Lane: Figures 7.18-7.19, 7.56-7.58, 7.66 Reproduced with the kind permission of Carr Lane Manufacturing Co Website: www.carrlane.com Email: info@carrlane.com

Stephen Keightley, Copyright & Licensing Manager, British Standards Institution: Table 8.1 Reproduced with the permission of the British Standards Institution under licence number 2002SK/0214 British Standards can be obtained from: BSi Customer Services, 389 Chiswick Road, London W4 4AL Website: www.bsionline.co.uk

Mia Amato, McGraw-Hill: Figures 1.19, 4.6 and Table 8.1 Case studies 1.2 and 2.1 Reproduced with permission of The McGraw-Hill Companies

Janice Cook, Marketing Manager, Mitutoyo (UK) Ltd.: Figures 8.25-8.31, 8.33 All pictures and diagrams used by kind permission of Mitutoyo (UK) Ltd., West Point Business Park, Andover, Hampshire, SP10 3UX Website: www.mitutoyo.co.uk

Chris Pockett, Group Marketing Director, Renishaw plc: Figure 8.34 Pictures reproduced with permission of Renishaw plc, New Mills, Wotton- under-Edge, Gloucestershire GL12 8JR Website: www.renishaw.co.uk Bob Lawrie, Head of Quality Improvement, The Society for Motor Manufacturers and Traders Limited, Forbes House, Halkin Street, London SW1X 7DS: Figures 8.14 and 8.15 and charts in Appendix B The charts used in the above figures and Appendix B are based on material in

Guidelines to Statistical Process Control, 2nd edition- An Introduction to Charting edited by Neville Mettrick, published 1994 by The Society of

Motor Manufacturers and Traders Limited who have granted permission for their reproduction Website: www.smmt.co.uk

Thomson Learning: Figures 5.6 and 5.7 From Modern Manufacturing Processes, 1 st edition by D.L Goetsch 9 1991 Figures 7.20-7.24 From Jig and Fixture Design, 4th edition by E Hoffman 9 1996 Reprinted with

permission of Delmar Learning, a division of Thomson Learning: www.thomsonrights.com Fax: 800 730-2215

Kathleen Robbins at John Wiley & Sons, Inc: Figures as indicated in main text

Pearson Education Limited: Figures as indicated in main text

Personal There are a huge number of people whom I would like to thank:

The staff at Butterworth-Heinemann for their advice and especially their patience, particularly Clare Harvey and Rebecca Rue Isobel Brown for the typing contributions; John Hunter, Jim Thomson, Steve Gallagher and James Findlay - if you don't laugh you'll cry! Anne and Peter Scallan Snr (Mum and Dad) for giving me support when I needed it most Jacky and Ronnie Matheson and family, Claire and Keith Hanson, Alan and Muriel Hall, Stephen Hanson-Hall for being my 'brother' (look after him Charlotte !) and Matthew Hanson (get out of bed!)

Last and by no means least, my family Love to my daughters Lauren, Carly, Rachel, Rachel (not a misprint- two Rachels!) and Sarah- thanks for giving me grey hair; to Janet for giving me the time to get my head together and being the rock upon which I have rebuilt my life In the words of the modern poet John 'Ozzy' Osbourne, 'I love you all more than life itself, but you all drive me mad!'

Table of Contents

Preface Acknowledgements

App A Control chart factors for variables

App B Blank control charts

App C Blank process planning documents

Index

1 Introduction to manufacturing

1.1 Introduction The prosperity of human kind has been inextricably linked with the ability to

use and work with the available materials and tools throughout history Indeed, there is archaeological evidence of man's toolmaking ability dating

as far back as 2-3 million years (Mair, 1993) However, the basis for manu- facturing as we know it today can be traced as far back as 5000-4000 BC, with the manufacture of artefacts from materials such as wood, stone, metal and ceramics (Kalpakjian, 1995) The modem manufacturing organization, based on the factory system and the division of labour, was borne of the Industrial Revolution of the eighteenth century The roots of modem manu- facturing processes can also be traced to the late eighteenth century with the development of the cotton gin by Eli Whitney in the United States (Amstead

et al., 1987) and the first all metal lathe by Henry Maudsley in the United Kingdom in 1794 (DeGarmo et al., 1988) The development of manufactur- ing processes continued in the early part of the nineteenth century with the introduction of a loom automatically controlled by punched cards in France

in 1804, the development of the milling machine by Whitney and the use of mass manufacturing techniques by Marc Isambard Brunel in 1803 in the United Kingdom (Mair, 1993)

The development of manufacturing industries to this day still relies heavily

on research into manufacturing processes and materials and the development

of new products Those countries that have been at the forefront of the devel- opment of manufacturing have come to be known as the developed countries,

while those that have very little manufacturing are considered underdeveloped

(el Wakil, 1989) This ability to manufacture products has a huge beating on the wealth and prosperity of a country In theory, the greater the ability of a country to manufacture, the wealthier that country should be (how this is achieved is discussed later in this chapter) Prime examples of this type of country are the United Kingdom and the United States For example, in the United Kingdom, manufacturing still makes a significant contribution to the wealth and prosperity of the nation, despite the decline of manufacturing in the 1980s A recent government report estimated that there are 4.3 million people directly involved in manufacturing and account for 20 per cent of the

Gross Domestic Profit or GDP (DTI, 1999) Similarly, figures for the United States estimate that approximately 17.8 million people are employed in man- ufacturing (van Ark and Monnikhof, 1996) and again account for around 20 per cent of GDP (BEA, 1998) However, for the likes of the United Kingdom and the United States to remain competitive in the global market, the resources employed in manufacturing must be used in the most cost effective manner This means that the manufacturing of the products must be planned to make best use of these resources, which is the very essence of process planning

2 Process Planning

1.2 Aims and objectives The aims of this chapter are to define manufacturing and present the main types

of manufacturing systems employed and their operational characteristics

On completion of this chapter, you should be able to:

9 define the manufacturing activity;

9 state the main goals of a manufacturing organization;

9 define the Principle of Added Value;

9 define a manufacturing system;

9 identify and describe the common manufacturing systems and their oper- ational characteristics;

9 identify and describe the main processing strategies and relate them to the common manufacturing systems;

9 identify and describe the main roles and responsibilities of a manufacturing engineer

1.3 What is

manufacturing?

In the introduction to this chapter the importance of manufacturing to the wealth and prosperity of a country was explained However, before proceed- ing, the question 'What is manufacturing?' has to be answered

Although the basis of manufacturing can be traced back as far as 5000-4000 BC, the word manufacture did not appear until 1567, with manu- facturing appearing over 100 years later in 1683 (Kalpakjian, 1995) The word was derived from the Latin words manus (meaning 'hand') and facere

(meaning 'to make') In Late Latin, these were combined to form the word

manufactus meaning 'made by hand' or 'hand-made' Indeed, the word factory was derived from the now obsolete word manufactory In its broadest and most general sense, manufacturing is defined as (DeGarmo

et al., 1988):

the conversion of stuff into things

However, in more concise terms, it is defined in the Collins English Dictionary (1998) as:

processing or making (a product) from raw materials, especially as a large scale operation using machinery

In a modem context, this definition can be expanded further to:

the making of products from raw materials using various processes, equipment, operations and manpower according to a detailed plan During processing, the raw material undergoes changes to allow it to become

a part of a product or products Once processed, it should have worth in the market or a value Therefore, manufacturing is 'adding value' to the material The value added to the material through processing must be greater than the

Finally, the income of an organization, calculated by deducting the total costs from the sales revenue, is also sometimes referred to as the added value or value added (Gilchrist, 1971) In fact, in the past organizations have used bonus or incentive schemes for employees based on this definition of value added However, in the context of this book, the ICMA (1974) definition will

be used when referring to added value Therefore, using this definition, a manufacturing organization will only be successful if it not only makes prod- ucts, but also sells them This allows manufacturing to be further defined as: the making of products from raw materials using various processes, equipment, operations and manpower according to a detailed plan that

is cost-effective and generates income through sales

This definition adds the dimension of the processing being cost-effective

This is illustrated in Fig 1.1 There is no one concept that will cover all indus- tries in detail Therefore, the concept defined above is generic However, there are numerous detailed definitions of what represents a manufacturing system One such definition that is particularly appropriate is that of Lucas Engineering and Systems This defines a manufacturing system as (Lucas Engineering and Systems, 1992):

an integrated combination of processes, machine systems, people, organi- zational structures, information flows, control systems and computers whose purpose is to achieve economic product manufacture and inter- nationally competitive performance

Figure 1.1 Basic model of manufacturing system adding value

1.5 Inputs and outputs

of a manufacturing

system

Generally, the input/output analysis of a manufacturing system will be as shown in Fig 1.2 It can be seen from this that the system does not have an influence or control over all the inputs, for example, social pressures This means that the system must be flexible enough to deal with input variations

It must also be able to cope with the rapid changes in technology and the market, particularly as product life cycles become increasingly shorter (Evans, 1996)

The main output of the manufacturing system is obviously the product or manufactured goods These can be classified as either consumer products or

producer products Consumer products are those that are sold to the general public However, producer products are those which are manufactured for other organizations to use in the manufacture of their products, which in turn could be either of the above categories of product Therefore, in some instances, the output of one manufacturing system is the input of another Thus, there may be considerable interaction between systems Finally, it should also be noted that not all the outputs are tangible or measurable For example, how is reputation measured although it can have a marked effect on the manufacturing system?

Figure 1.2 Inputs and outputs of a manufacturing system

1 All systems will have specific business objectives to meet in the most cost-effective manner

2 All systems consist of an integrated set of sub-systems, usually based on functions, which have to be linked according to the material processing

3 All systems must have some means of controlling the sub-systems and the overall system

4 To operate properly, all systems need a flow of information and a decision-making process

All of the above must be incorporated into the manufacturing system to allow stable operation in the rapidly changing global market in which most organizations compete Each organization has its own unique manufacturing system, developed to support its specific objectives and deal with its own unique problems However, the sub-systems within each can be represented

as shown in Fig 1.3 It is clear from the figure that the sub-systems are built

Market Product need

(Identified by market research)

Figure 1.3 The manufacturing system (Mair, 1993)

6 Process Planning

around the main functions or departments of the organization and these can

be further broken down This aspect of manufacturing organization will be considered further in Section 1.8

1.7 Developing a

manufacturing strategy

As stated previously, all manufacturing systems have specific business objectives to be achieved, which are driven by the organizational mission statement These business objectives are then used to generate the business strategy The business strategy should be developed to allow the organiza- tion to meet its business objectives but be flexible enough to accommodate

change The business strategy in turn is used to formulate both the market-

ing strategy and the manufacturing strategy Finally, the implementation of

these strategies will require people and processes as illustrated in Fig 1.4 The manufacturing strategy can be defined as a long range plan to use the resources of the manufacturing system to support the business strategy and

in turn meet the business objectives (Cimorelli and Chandler, 1996) This in turn requires a number of decisions to be made to allow the formulation of the manufacturing strategy Six basic decision categories have been identi- fied and these are (Hayes and Wheelright, 1984):

Capacity decisions - these deal with how customer demand is met in terms

of the resources available and those required In effect the questions being asked are, what has to be made, what will be used to make it and when and how will this be achieved?

Process decisions - this is basically about deciding which type of system

should be employed This is complicated by the fact that most companies employ hybrid systems This decision is linked to four distinct processing strategies that are discussed in Section 1.10

Figure 1.4 Developing a manufacturing strategy

I n t r o d u c t i o n to m a n u f a c t u r i n g 7

factory level, and the assigning of specific products to specific plants at an organizational level The types of plant layout that can be used will be con- sidered further in Section 1.11

made inhouse and what is to be sub-contracted This is particularly important

as it will influence the capacity, facilities and process decisions This will be discussed further in Chapter 9

tion required to meet the business objectives Specifically it will consider the production planning and control system, the quality assurance system (con- sidered further in Chapter 8) and the organizational structure

huge influence on this decision The two main decisions are identifying the functions and organizational structure required (both of which are consid- ered further in Section 1.8) and the reward system, that is, pay, bonuses, etc All of the above will be considered further to some extent in this book In the remainder of this chapter the facilities decisions, process decision, infrastructure decision and, in part, the human resource decision, will be discussed further

1.8 Manufacturing

organizational structures

In Section 1.4, it was explained that the sub-systems of the manufacturing system are based on the functions or departments within the organization The organization of these functions plays an important role in the achieve- ment of the system objectives Therefore, once the functions required have been identified, the most appropriate organizational structure must be employed to help achieve the system objectives

1.8.1 Typical functions in a manufacturing organization

Although every manufacturing organization is unique in some respect, there are six broad functions that can be identified in almost any manufacturing organization These are sales and marketing, engineering, manufacturing, human resources, finance and accounts and purchasing The general respon- sibilities of these functions are as follows:

with the market The main responsibilities of this function are to ensure a steady flow of orders and consolidate and expand the organization's share of the market Typical sub-functions might include sales forecasting, order pro- cessing, market research, servicing and distribution

include product design, research and development (R&D) and the setting of specifications and standards The level to which R&D is carried out will depend

on the product For example, in high-tech products, R&D will play a major role

in determining the use of materials and processes and future product design

8 P r o c e s s P l a n n i n g

very much on the size of the organization Typical sub-functions might include:

plans such as the m a s t e r p r o d u c t i o n s c h e d u l e (MPS) and the m a t e r i a l s

to the required specification

and machinery is maintained at an appropriate level for its use

work methods and standards, plant layouts and cost estimates

ing systems development, process development, process evaluation and process planning

work through the manufacturing plant (work-in-progress) Stores will usually be included in this function

sub-functions such as recruitment, training and development, labour rela- tions, job evaluations and wages

financing, budget setting and investment analysis Accounts generally deal with the keeping of financial records including cost accounting, financial reporting and data processing

and services They must ensure that the above support the manufacturing capabilities by satisfying their supply need They must also ensure the qual- ity and quantity of supplies through vendor rating

1.8.2 Types of organizational structure

How the above functions are represented within an organization will depend mainly on the size of the organization For example, in a small organization some of these functions may be combined such as purchasing and finance and accounts However in a large organization there may be further diversification

of functions, creating more departments such as sales and marketing being large separate departments How these are organized will also depend on a number of factors These will include, among others, the size of the organiza- tion, how many facilities/locations there are within the organization, the com- plexity of the products being manufactured and the variety of products manufactured Finally, the 'style' of management employed, that is, central- ized or decentralized, will be a major factor in the type of structure employed

In an organization with a centralized structure, management responsibility

Introduction to manufacturing 9

and authority is held within the upper levels of the organization However, in

a decentralized structure, some of the responsibility and authority is pushed down to the lower levels This allows decisions to be made at the levels most affected by them It also frees senior management from the day-to-day decision-making Taking all of the above into account, there are three basic organizational structures employed in manufacturing (Coward, 1998):

II Managing Director

-Production _ Recruitment I Finance I planning

Training and Capital

- Quality development finance assurance Industrial

- Plant relations Budgeting maintenance Investment -Industrial analysis engineering

- Manufacturing engineering

- Production control

- Production

IAccounts I Cost accounting Financial reporting Data processing

Figure 1.5 A functional structure

I

Purchasing

t Buying Vendor rating

I

Laptop division

t Engineering Manufacturing

I

Finance and accounts

-Capital finance

- Budgeting -Investment analysis -Cost accounting

- Financial reporting

- Data processing

I

Group services

- Market research

- Service and distribution

I

Human resources Recruitment Training and development Industrial relations

Product structure

Many large manufacturing organizations produce a diverse range of prod- ucts In such organizations, it is common to employ a structure based on the products manufactured, that is, a product structure This generally means splitting the organization into product divisions, all of which incorporate the functions required to manufacture the specified product However, indirect functions such as sales and marketing, finance and accounts, human resources and purchasing will generally be shared across the group Each division will also tend to act as an autonomous business unit The main advantage of this approach is that the required product expertise is incorporated into a single part of the organization However, the main disadvantage is the duplication

of functions across divisions as illustrated in Fig 1.6 Finally, product struc- tures tend to employ a decentralized management style

Matrix structure

In essence, a matrix structure is an attempt to obtain the benefits of both func- tional and product structures This is based on one manager being responsible for functions and products in one area and is similar to the product structure

in this respect However, the main difference is that the matrix groupings are temporary This is to allow the resources for each group to be changed This

is based on a continuous review of resources carried out to ensure that the allocation of resources is appropriate for each group Ultimately, this gives

Introduction to manufacturing 11

Figure 1.7 A matrix structure

the matrix structure more flexibility than the product structure Finally, the management style employed in a matrix structure is decentralized An exam- ple of such a structure is illustrated in Fig 1.7

1.8.3 Organizational management levels

Within all manufacturing organizations there are usually three distinct levels

of management These are referred to as strategic, tactical and operational management

Strategic level- this level is usually associated with senior management This

involves the setting of short- and long-term business objectives that will give the organization a competitive advantage over other similar organizations

Tactical l e v e l - this level is associated with middle management The main

function of this level is to develop the plans by which the business objectives can be met using the organization's resources

Operational level- this level is the fronfline management and the main function

of this level is to ensure the everyday operations are planned and monitored

1.9 Categories of

manufacturing system

There are two basic categories of manufacturing system:

9 discrete parts manufacturing;

9 continuous process manufacturing

Discrete parts manufacturing involves the manufacture of individual items and can be further classified into:

9 project manufacture;

9 jobbing shop manufacture;

1.9.1 Project manufacture

The defining feature of project manufacture is the type of layout employed and the fact that there is a very low production rate, that is, not many units produced The layout is known as a fixed position layout In the fixed posi- tion layout, the product remains at the same location, that is, a fixed position, usually due to the size/weight of the product The workers and all tools and equipment are then brought to the product to carry out work It should be noted that component parts, sub-assemblies and assemblies might be manu- factured elsewhere and then brought to the product location The workers are usually highly skilled and material handling is high It is also common for products manufactured using this layout to be one-of-a-kind, for example, ships, aircraft, space vehicles, bridges, buildings, etc This approach to manu- facture offers a number of advantages:

9 there is reduced material movement;

9 used with a teamwork approach it can improve continuity of operations;

9 it is flexible in terms of coping with changes in product design, changeovers and volume

There are also a number of disadvantages:

9 increased movement of personnel and processing equipment;

9 may require duplication of processing equipment;

9 increased work-in-progress;

9 increased space requirements

This is, in effect, a specialist job shop environment

1.9.2 Jobbing shop manufacture

The jobbing shop's distinguishing feature is the production of a wide variety

of products Manufacture is very often specific to customer order and specifi- cation This usually means very small lot sizes and very often the production

of one of kind However, some job shops manufacture to fill finished goods inventories As a wide variety of products are produced, a wide variety of manufacturing processes is required The product variety also means that the workforce must be highly skilled in order to fulfil a range of different work

Introduction to manufacturing 13

assignments Typical products of job shops are special purpose machine tools, fabricated sub-assemblies and components for the aerospace industry Within job shops, production equipment is usually general purpose and generally arranged according to the general type of manufacturing process For example, the lathes are in one department, milling machines in another

and drill presses in still another and so forth This is known as a process -r

focused layout and allows the job shop to make such a wide variety of prod-

ucts Each different part requires its own unique sequence of operations and therefore requires to be routed through the manufacturing system by means

of a routing sheet In general, forklifts and handcarts are used to move material from one process to another It is estimated that as much as 75 per cent

of discrete part manufacture is made in lots of 50 (DeGarmo et al., 1988) or

less Thus, the job shop system is an important method of manufacture

1.9.3 Batch manufacture

The main feature of batch manufacture is the production of medium size lots

of a product in either single runs or repeated runs at given times The lot size range is approximately 5-1000 and even possibly more Again, as the prod- uct variety can be high, the number of processes required is high and there- fore the equipment is general purpose Similar to job shop manufacture, the workforce must be skilled and flexible to cope with the high product variety The process-focused organization of the job shop is also equally applicable for batch production Therefore job and batch manufacture are often con- fused because they have the following common characteristics:

9 the flow of manufacture will be intermittent;

9 some parts will be for customer orders and others for stock;

9 schedule control of orders will be required to ensure delivery times are met;

9 there is a high product variety

To differentiate between job and batch manufacture, it is not the number

of components that is the deciding factor, but the organization of the manu- facture itself For example (Timmings, 1993), consider the manufacture of one lot of five components These could be made by five operators with each making a component outright This is what would normally happen in a job shop However, each component could be passed from operator to operator with each specializing and completing a particular operation In this case, the manufacture would be classified as batch production

1.9.4 Flow/mass manufacture

The main characteristic of flow line manufacture is the high volume of prod- ucts produced It is usually referred to as mass manufacture due to the very large quantities of products manufactured It is also common for mass manu- facture systems to have high production rates

With regards to the process equipment this tends be of a specialized nature, with processes being dedicated to a particular product In fact, very

14 Process Planning

often processes are designed exclusively to produce a particular product This means that investment in specialized machines and tooling is high The skill level of the workforce tends to be lower than that of both job and batch manu- facture This is due to the fact that the manufacturing skill is transferred from operator to machine through the specialist nature and design of equipment Products flow through a sequence of operations by material-handling devices such as conveyors and other transfer devices They move through the operations one at a time with the time at each process fixed In flow line manu- facture, the organization of the process equipment is product focused In this type of manufacturing system, the equipment is arranged in order of the product's sequence of operations This means that equipment is arranged in

a line with generally only one of each type of process The exception to this

is where duplicates are needed to balance the time taken for a particular product The line is organized to make a single product or a regular mix of products

1.9.5 Cellular manufacturing

A cellular manufacturing system is usually composed of a number of linked cells The cells themselves usually compose of a number of grouped processes These are normally grouped according to the sequence and opera- tions needed to make a particular component part, sub-assembly or product The arrangement within the cell is much like that of a flow system, but it is more flexible Cells are normally laid out in a U-shape so that workers can move from machine to machine, loading and unloading parts Usually there are high levels of automation within cells, including all machines being capable of running unattended and switching themselves off after the machin- ing cycle is complete This also allows the operators to carry out manual oper- ations such as finishing and inspection or walk from machine to machine

To implement a cellular manufacturing system, the current system must be converted in stages This will entail taking parts of the current system and converting it into cells The cells should be designed in such a way as to allow the manufacture of specific groups or families of parts, that is, parts which have the similar geometrical features and require the same manu- facturing processes to make One method used in converting traditional manufacturing, particularly the jobbing shop, to cellular manufacturing is

group technology This is a technique that helps group parts into compatible families

Cells are generally linked directly to each other or to assembly points They can also be indirectly linked by the pull inventory system known as

Kanban Finally, the cells can be linked in such a way as to allow the syn- chronous operation with sub-assembly and final assembly lines With regards

to the workforce, it may be the case that they move around the cells employ- ing different processes Therefore, workers are usually required to be multi- functional

Cellular manufacturing has many features that make it different from the traditional manufacturing systems Parts usually move one at a time from machine to machine instead of in batches When a cell worker completes a journey round the cell a part should have been completed Set-up times also tend to be shorter than for traditional systems The lead times for parts and